The present invention generally relates to loudspeaker systems and more particularly to systems and method of equalizing the frequency response of loudspeaker systems.
Equalization is a well-known and widely used process of adjusting the frequency response of a loudspeaker. To “equalize” a loudspeaker system is to adjust the amplitude of the audio signal a different frequencies within the system's operating frequency range in order to correct for frequency dependent distortions and anomalies that appear in the frequency response of the system. Distortions in the frequency response can, for example, be introduced by components of the loudspeaker system itself or by the acoustic environment in which the system is used. Equalization can also be used to adjust the frequency response to achieve a desired audio experience, for example, to create a particular sound for a particular performance at a particular venue.
Equalizers are implemented using linear filters that alter the frequency response of the loudspeaker system within specific bands of frequencies. Different filtering techniques have been devised, each providing different capabilities. Standard first order shelving filters are often used for basic treble and bass controls in consumer products.
For more sophisticated applications, control is increased by increasing the number of frequency bands that can be manipulated by the user. The more bands the more control. And the more controllable each band is the greater the capability is to fine tune the frequency response. With conventional equalization schemes the gain (cut or boost) within each frequency band gain can be readily controlled. However, this is not true with the shape of the bands at the bands break point frequencies. Each break point will be characterized by a slope, typically specified in terms of dB/octave and the shape of the band can be adjusted by adjusting this slope. The slope will be relatively gradual where lower order liken; are used and will become increasingly steep as the order of the filters increases. Control over the shape of the bands would give the operator increased flexibility to fine tune the system's frequency response to achieve desired sonic experiences. However, with conventional equalization schemes, user adjustments to the slope at the frequency break points cannot be made without simultaneously changing the band gain, an unworkable condition in practice. This limits the equalizer's capability to render fine adjustments in the response of an audio system.